With an image forming apparatus that forms an image by an electro-photographic method, in general, an image is formed of a toner of fine particles on a sheet; the toner on the sheet is melt by heat-pressing in a fixing device to be fixed as a toner image; and the sheet is ejected or transported to a post-processing device.
In recent years, high speed printing has been enabled, and a sheet is transported to a post-processing device for binding processing before the sheet on which an image having been fixed is not cooled sufficiently, which causes a problem of generating uneven glossiness (uneven waxing) of a toner image in the process where the sheet passes through the conveying path in the post-processing device, when, for example, the sheet is pinched by conveying rollers.
To avoid this problem, the following methods are disclosed.
1) A method that passes a sheet through sheet-cooling rollers which are formed of heat-pipes, at a lower conveying speed than that during the time the sheet passes through a fixing device, and thereby lowers the temperature (refer to Unexamined Japanese Patent Application Publication No. H10-254285, for example).2) A method that cools a sheet fed out from a fixing device in the main body of an image forming apparatus, while a belt cooled by a cooling fan sucks and conveys the sheet (refer to Unexamined Japanese Patent Application Publication No. 2004-198863, for example).
However, since cooling means is arranged in the main body of an image forming apparatus and it is necessary to secure a conveying space to be used after a fixing process, these methods have shortcomings of a larger size of the apparatus main body and an increase in cost due to a cooling fan, heat roller, conveying belt, sucking unit, etc.